The present invention relates to a semiconductor module and a semiconductor device containing the semiconductor module or a semiconductor chip. Incidentally, the expression “semiconductor module” means to include at least a semiconductor chip hereinafter.
In general semiconductor devices each containing a semiconductor module for use in power modules, the semiconductor module is closely adhered or soldered on a heat radiating member for radiating the heat generated from the semiconductor module.
Usually, in each of the semiconductor devices that employs the closely adherence structure of the semiconductor module on the heat radiating member, a grease member with excellent heat conductivity is applied on at least one of a contact surface of the semiconductor module and that of the heat conductive member, which are opposite to each other.
The grease member allows the heat conductivity between the semiconductor module and the heat radiating member to improve because the contact surfaces of the semiconductor module and the heat radiating member are fine uneven.
The structure in which the grease member is applied on the at least one of the contact surfaces of the semiconductor module and the heat radiating member is referred to simply as “grease application structure”.
As an example of the semiconductor devices each with the grease application structure, the semiconductor device in which a single-phase inverter circuit for controlling an AC (alternate current) motor is built has been disclosed in U.S. Patent Publication 6542365 (Japanese Patent Publication 2001-308263).
The disclosed semiconductor device comprises a semiconductor module containing a single-phase circuit of a three-phase inverter circuit, that is, a half-bridge circuit, which is made modular.
In the semiconductor module, a first semiconductor chip constituting an upper arm of the single-phase circuit and a second semiconductor chip constituting a lower arm thereof are mounted on a middle-sided plate with heat and electric conductivity, middle-sided plate which is served as an AC terminal of the single-phase circuit. The first and second semiconductor chips are adjacently arranged in a longitudinal direction of the middle-sided plate.
A high-sided plate having heat and electric conductivity and constituting a high-sided terminal of the three-phase inverter circuit is disposed on the first semiconductor chip, and a low-sided plate having heat and electric conductivity and constituting a low-sided terminal of the three-phase inverter circuit is disposed on the second semiconductor chip. Resin is molded in the module to cover both side surfaces of the first and second semiconductor chips, the high-sided-plate, the low-sided-plate and the middle-sided-plate, respectively.
Then, in the disclosed semiconductor device, the upper surface of the semiconductor module (each of the upper surfaces of the high-sided plate and low-sided plate), on which a grease layer as the grease member is coated, is closely contacted to a first heat sink as the heat radiating member. In addition, the lower surface of the semiconductor module (the lower surface of the low-sided plat), on which a grease layer as the grease member is coated, is also closely contacted a second heat sink as the heat radiating member.
That is, the disclosed semiconductor device allows the semiconductor modules to be cooled from both upper and lower surfaces of each module.
To keep high each heat conductivity of each conventional semiconductor device with the grease application structure is necessary to apply the grease member as thin as possible on the at least one of the contact surfaces of each semiconductor module and each heat radiating member within the range that allows the applied grease member to be sufficiently filled in the fine uneven portions of the at least one of the contact surfaces and to compensate for the warp therein.
In the manufacturing process of each semiconductor device with the grease application structure, therefore, the grease member is coated on the at least one of the contact surfaces of the semiconductor module and the heat radiating member, and the contact surfaces of the semiconductor module and the heat radiating member are closely contacted to each other and are subjected to pressure in the contacting direction. The application of pressure to the laminated semiconductor module and the heat radiating member permits excess grease member to be driven out, thereby making thin the thickness of the grease member interposed between the contact surfaces of the semiconductor module and the heat radiating member as thin as possible.
The portion of the excess grease member especially located at the center portion of each contact surface needs to be driven out to the peripheral portion of each contact surface, but this driving out of excess grease member is difficult so that the excess grease member, which must be extruded, remains between the contact surfaces of the semiconductor module and the heat radiating member, causing the radiating ability of the semiconductor module to decrease.
If reducing the amount of grease member to be applied on the at least one of the contact surfaces of the semiconductor module and the heat radiating member to avoid the occurrence of the excess grease member, it is difficult to endure high heat conductivity between the semiconductor and the heat radiating member in cases where the at least one of the contact surfaces thereof has large unevenness and/or a large warp.
In contrast, if the thickness of the applied grease member on the at least one of the contact surfaces is too large, this causes the deterioration of the heat conductivity between the contact surfaces of the semiconductor module and the heat radiating member so that bubbles may occur therebetween.
Especially, in addition to the above issues, the disclosed semiconductor device may be apt to cause creepage discharge between the high-sided plate and the low-sided plate.